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United States Patent |
5,193,963
|
McAffee
,   et al.
|
March 16, 1993
|
Force reflecting hand controller
Abstract
A universal input device for interfacing a human operator with a slave
machine such as a robot or the like includes a plurality of serially
connected mechanical links extending from a base. A handgrip is connected
to the mechanical links distal from the base such that a human operator
may grasp the handgrip and control the position thereof relative to the
base through the mechanical links. A plurality of rotary joints is
arranged to connect the mechanical links together to provide at least
three translational degrees of freedom and at least three rotational
degrees of freedom of motion of the handgrip relative to the base. A cable
and pulley assembly for each joint is connected to a corresponding motor
for transmitting forces from the slave machine to the handgrip to provide
kinesthetic feedback to the operator and for producing control signals
that may be transmitted from the handgrip to the slave machine. The device
gives excellent kinesthetic feedback, high-fidelity force/torque feedback,
a kinematically simple structure, mechanically decoupled motion in all six
degrees of freedom, and zero backlash. The device also has a much larger
work envelope, greater stiffness and responsiveness, smaller stowage
volume, and better overlap of the human operator's range of motion than
previous designs.
Inventors:
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McAffee; Douglas A. (San Pedro, CA);
Snow; Edward R. (Sandy Hook, CT);
Townsend; William T. (Somerville, MA)
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Assignee:
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The United States of America as represented by the Administrator of the (Washington, DC)
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Appl. No.:
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608658 |
Filed:
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October 31, 1990 |
Current U.S. Class: |
414/5; 414/7 |
Intern'l Class: |
B25J 003/00 |
Field of Search: |
414/5,7,222
|
References Cited
U.S. Patent Documents
2978118 | Apr., 1961 | Goertz et al. | 214/1.
|
3631737 | Jan., 1972 | Wells | 74/469.
|
4221516 | Sep., 1980 | Haaker et al. | 414/5.
|
4259876 | Apr., 1981 | Belyanin et al. | 74/469.
|
4392776 | Jul., 1983 | Shum | 414/744.
|
4566843 | Jan., 1986 | Iwatsuka et al. | 414/680.
|
4805477 | Feb., 1989 | Akeel | 74/479.
|
4883400 | Nov., 1989 | Kuban et al. | 414/5.
|
4950116 | Aug., 1990 | Nishida | 414/5.
|
Other References
Johnson et al., "Teleoperators and Human Augmentation," An AEC-NASA
Technology Survey, NASA SP-5047, Dec. 1967.
Bejczy et al., "Controlling Remote Manipulators Through Kinesthetic
Coupling," Computers in Mechanical Enginnering, Jul. 1983, pp. 48-60.
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Primary Examiner: Huppert; Michael S.
Assistant Examiner: Underwood; Donald W.
Attorney, Agent or Firm: Kusmiss; John H., Jones; Thomas H., Miller; Guy M.
Goverment Interests
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a
NASA contract, and is subject to the provisions of Public Law 96-517 (35
USC 202) in which the Contractor has elected not to retain title.
Claims
What is claimed is:
1. A universal hand controller device for interfacing a human operator with
a slave machine such as a robot comprising:
a base;
a plurality of serially connected mechanical links extending from the base,
the mechanical links being arranged into a first group of first, second,
and third linear position links and a second group of first, second, and
third angular position links;
a handgrip connected to the serially connected mechanical links distal from
the base such that a human operator may grasp the handgrip and control the
position of the handgrip relative to the base through the serially
connected mechanical links;
a plurality of rotary joints arranged to connect the mechanical links
together to provide at least three translational degrees of freedom and at
least three rotational degrees of freedom of motion of the handgrip
relative to the base, there being one rotary joint corresponding to each
degree of freedom, each rotary joint having a drive mechanism comprising a
drive motor, a drive pulley assembly and a drive cable connected between
the drive motor and the drive pulley assembly such that each joint is
cable driven;
means for mounting the drive motors for driving the rotary joints
corresponding to the rotational degrees of freedom to one of the linear
position links such that the drive cables in the drive mechanisms for the
rotary joints corresponding to the rotational degrees of freedom pass
through at least one rotary joint corresponding to the linear position
link upon which the drive motors for driving the rotary joints are
mounted; and
means for guiding the drive cable for the first, second, and third angular
position links parallel to an axis of rotation of a third of the rotary
joints.
2. The universal hand controller device of claim 1 additionally comprising
means for guiding the drive cable for the second and third angular
position links along an axis of rotation of a fourth of the rotary joints.
3. The universal hand controller device of claim 2 additionally comprising
means for guiding the drive cable for the third angular position link
along an axis of rotation of a fifth of the rotary joints, wherein the
drive mechanism for each rotary joint is kinematically decoupled from all
of the other rotary joints such that motion of the handgrip about any
selected joint causes no motion of the handgrip relative to any of the
other joints.
4. The universal hand controller device of claim 3 wherein rotation of the
third linear position link about the third joint causes a uniform twist in
the cables for the fourth, fifth, and a sixth of the joints.
5. The universal hand controller device of claim 4 wherein the motors for
driving the third, fourth, fifth, and sixth joints are remotely located
from the corresponding rotary joints and wherein the drive cables for each
rotary joint have constant length as rotation occurs about any of the
rotary joints.
6. A universal hand controller device for interfacing a human operator with
a slave machine such as a robot, comprising:
a base;
a plurality of serially connected mechanical links extending from the base,
the mechanical links being arranged into a first group of linear position
links and a second group of angular position links;
a handgrip connected to the third angular position link distal from the
base such that a human operator may grasp the handgrip and control the
position thereof relative to the base through the serially connected
mechanical links;
a plurality of rotary joints arranged to connect the mechanical links
together to provide three translational degrees of freedom and three
rotational degrees of freedom of motion of the handgrip relative to the
base, there being one rotary joint corresponding to each degree of
freedom, each rotary joint having a drive mechanism comprising a
corresponding a motor, a drive pulley assembly, and a drive cable
connected between the motor and drive pulley assembly such that each joint
is cable driven; the mechanical links and rotary joints including
a first linear position link rotatably mounted to the base by a first one
of the plurality of rotary joints;
a second linear position link rotatably mounted to the first linear
position link by a second one of the plurality of rotary joints;
a third linear position link rotatably mounted to the second linear
position link by a third one of the plurality of rotary joints;
a first angular position link rotatably mounted to the third linear
position link by a fourth one of the plurality of rotary joints;
a second angular position link rotatably mounted to the first angular
position link by a fifth one of the plurality of rotary joints;
a third angular position link rotatably mounted to the second angular
position link by a sixth one of the plurality of rotary joints, the first,
second, and third angular position links being arranged to have axes of
rotation that intersect at a point that is fixed with respect to the third
linear position link; and
means for mounting the drive motors for driving the fourth, fifth, and
sixth rotary joints to the third linear position link such that the drive
cables in the drive mechanisms for the fourth, fifth, and sixth rotary
joints pass through the axis of rotation of the third rotary joint;
wherein the drive cable for the first, second, and third angular position
links are parallel to the axis of rotation of the third rotary joint, the
drive cable for the second and third angular position links are guided
along the axis of rotation of the fourth rotary joint, and the drive cable
for the third angular position link is guided along the axis of rotation
of the fifth rotary joint, so that the drive mechanism for each rotary
joint is kinematically decoupled from all of the other rotary joints such
that motion of the handgrip about any selected joint causes no motion of
the handgrip relative to any of the other joints.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to apparatus and methods for controlling
robots or other similar devices. This invention relates particularly to
apparatus and methods that a human operator may use for manually
controlling a robot arm or other slave devices. Still more particularly,
this invention relates to establishing a kinesthetic coupling between the
operator and the robot by means of a manual control input device.
2. Background Art
Although robotics is a rapidly developing field, for decades to come there
will be many applications and tasks that are far too complex and
unstructured to be performed completely by unsupervised autonomous robots.
Therefore, the need for direct human supervision and control of advanced
robotic systems will continue. This is true both in space applications and
in terrestrial applications, such as undersea exploration, remote defense
technologies, and various tasks in the nuclear industry. Often it is
necessary to have the human operator physically removed from the actual
work site, remotely supervising and guiding the robot in the performance
of a difficult or dangerous task. Remote manipulation is essential when
barriers, distances or environmental hazards separate the human operator
from a task to be performed. One of the key problems facing the designers
of human-supervised robotic systems is how to interface human operators
with these complex remotely operated machines.
Researchers have worked for many years to develop a useful, intuitive
interface between human operators and teleoperated machines. In general, a
teleoperator is any device that allows humans to manipulate or examine
objects and environments remotely. In the late 1970's, J. K. Salisbury
collaborated with A. K. Bejczy of the Jet Propulsion Laboratory to develop
a force reflecting master for use in bilateral control of teleoperated
systems. Reference is made to Bejczy and Salisbury, Kinesthetic Coupling
Between Operator and Remote Manipulator, Proceedings of the International
Computer Technology Conference, ASME, August, 1980 and to Bejczy and
Salisbury, Controlling Remote Manipulators Through Kinesthetic Coupling,
Computers in Mechanical Engineering, July, 1983, pp. 48-60, which describe
the work of Salisbury and Bejczy. A manual hand controller input device is
presently necessary for a human operator to control teleoperated machines.
A hand controller generally includes a plurality of structural members
connected at joints that permit relative movement of the members as an
operator moves a handgrip. As the operator moves the handgrip around in a
defined work envelope, a control computer reads signals indicative of
movements of each member and calculates the position of the handgrip
relative to a defined reference. The computed information is then used to
control the corresponding motion of the remote manipulator. The signals
indicative of movements of the handgrip are typically transmitted to the
control computer by sensors included in the hand controller.
Forces and torques applied by a telemanipulator in a remote work site may
be sensed by various techniques. For example, a force/torque sensor may be
mounted on the end of the telemanipulator to directly measure the forces
and torques encountered. Each axis on the hand controller may have a motor
associated therewith, which means that a six degree of freedom system has
six motors.
The measured values of the forces and torques are transmitted to a control
computer that is connected to the hand controller. The control computer
transforms the force and torque signals into appropriate pulse width
modulated signals to drive the six motors of the hand controller and
reproduce a scaled representation of the forces and torques encountered in
the remote work site. The human operator thus appears to feel the forces
and torques exerted by the environment on the manipulator.
Forces and torques may be determined by a position disparity technique,
which relies upon the relative disparity between the position commanded
and the actual position achieved by the remote manipulator. Therefore, if
the manipulator strikes a fixed object in the environment, there is a
corresponding difference in the commanded position and the actual position
of the manipulator. A force proportional to the magnitude of the disparity
is generated in the hand controller.
SUMMARY OF THE INVENTION
This invention provides a new six-degree-of-freedom universal
force-reflecting hand controller (FRHC) for use as the man-machine
interface in teleoperated and telerobotic systems. The invention is
characterized as a universal input device because the slave portion of a
teleoperator used with the present invention does not need to be a
kinematic equivalent of the master.
The FRHC according to the present invention provides a human operator with
a natural and intuitive means for interacting with and controlling
teleoperated systems. The features of this new design include excellent
kinesthetic feedback, high-fidelity force/torque feedback, a kinematically
simple structure, mechanically decoupled motion in all six degrees of
freedom, and zero backlash. In addition, the new design has a much larger
work envelope, greater stiffness and responsiveness, smaller stowage
volume, and better overlap of the human operator's range of motion than
previous designs.
A force reflecting hand controller according to the present invention
includes at least six rotary joints and no prismatic, or sliding, joints.
Motion about each joint is decoupled from motion about all the other
joints, which simplifies the control software.
The FRHC according to the present invention has low friction joints and low
mass. The mass of the FRHC is distributed to provide low inertia with
respect to all six degrees of freedom. The motors are located so as to
partially counter balance part of the weight of the links. The FRHC is
operable both on the earth and in zero-gravity environments without
modification.
Many future space operations will require the extensive use of robot
manipulators and servicesrs to assist astronauts and scientists in
exploring space and developing a space-based infrastructure. The present
invention facilitates the use of robots in all operational environments. A
human operator positions the mechanical arm of a remote robot by simply
grasping the FRHC's handgrip and moving it in a desired direction and at a
desired rate. The remote robotic arm responds by mirroring the operator's
movements.
A universal input device according to the present invention for interfacing
a human operator with a slave machine such as a robot or the like includes
a plurality of serially connected mechanical links extending from a base.
The mechanical links are arranged into a first group of linear position
links and a second group of angular position links. A handgrip is
connected to the mechanical links distal from the base such that a human
operator may grasp the handgrip and control the position thereof relative
to the base through the mechanical links. A plurality of rotary joints is
arranged to connect the mechanical links together to provide at least
three translational degrees of freedom and at least three rotational
degrees of freedom of motion of the handgrip relative to the base.
The universal input device according to the present invention may further
comprise a cable and pulley assembly corresponding to each joint such that
each joint is cable driven, and a motor connected to each cable and pulley
assembly for transmitting forces from the slave machine to the handgrip to
provide kinesthetic feedback to the operator. The cable and pulley
assemblies are formed such that any selected joint is kinematically
decoupled from all of the other rotary joints such that motion of the
handgrip that causes motion about any selected joint causes no motion of
the handgrip relative to any of the other joints.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing a force reflecting hand controller
according to the present invention in which a hand grip is connected to a
base by six serially connected mechanical links and six rotary joints;
FIG. 2 is a perspective view showing the force reflecting hand controller
of FIG. 1 from the reverse angle;
FIG. 3 is a perspective view illustrating a human operator using the force
reflecting hand controller and showing the force reflecting hand
controller rotated 90.degree. from the orientation shown in FIG. 1;
FIG. 4 is a perspective view of a base that may be included in the force
reflecting hand controller of FIGS. 1-3;
FIG. 5 is a perspective view showing a first link assembly that may be
included in the force reflecting hand controller of FIGS. 1-3;
FIG. 6 is illustrates the structure of an idler pulley assembly that may be
included in the force reflecting hand controller of FIGS. 1-3;
FIG. 7 illustrates the structure of a termination pulley that may be
included in the force reflecting hand controller of FIGS. 1-3;
FIG. 8 illustrates the structure of a tension equalizing pulley and tension
arm idler pulleys that may be included in the force reflecting hand
controller of FIGS. 1-3;
FIG. 9 is a perspective view showing a second link assembly that may be
included in the force reflecting hand controller of FIGS. 1-3;
FIG. 10 is a perspective view showing a portion of a third link that may be
included in the force reflecting hand controller of FIGS. 1-3 and showing
components that may be included in a rotary joint formed between the
second and third links;
FIG. 11 is a perspective view of a bearing plug assembly that may be
included in the rotary joint of of FIG. 10;
FIG. 12 is an exploded perspective view showing a tension arm and bushing
assembly that may be included in the joint of FIG. 10;
FIG. 13 is a perspective view showing the tension arm and bushing assembly
of FIG. 11 mounted on a shaft;
FIG. 14 is a perspective view showing a pulley bracket that may be included
in the third link and a handgrip gimbal assembly that may be included in
the force reflecting hand controller according to the present invention;
FIGS. 15A and 15B are perspective views of the handgrip gimbal assembly of
FIGS. 1-3;
FIG. 16 is a perspective view showing a reduction drive mechanism and
cabling that may be included in the joint of FIG. 10;
FIG. 17 is a perspective view illustrating cables and pulleys for two of
the joints included in the force reflecting hand controller of FIGS. 1-3;
FIG. 18 is a cut away perspective view in the plane of FIG. 18 illustrating
the passage of cables through the joint of FIG. 10; and
FIG. 19 is a cross-sectional view taken about line 19--19 of FIG. 1 to
illustrate the passage of cables through the joint of FIG. 10 from a
different angle than that of FIG. 18.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1-3, a force reflecting hand controller 30 includes a
gimbal-mounted handgrip 32 connected to a base 34 by a plurality of links
36-41. The links are serially connected at a plurality of rotary joints
42-47 so that the handgrip 32 has six degrees of freedom relative to the
base 34. Six degrees of freedom are necessary to permit an operator to
move the handgrip 32 in rotational and translational motion relative to
three mutually perpendicular axes. As explained in detail subsequently,
the links 36-38 and rotary joints 42-44 allow translational motion of the
handgrip 32 while the links 39-41 and the joints 45-47 allow angular
orientation of the handgrip 32.
Referring to FIGS. 1, 2 and 4, the base 34 includes an opening 50 where the
rotary joint 42 connects the link 36 to the base 34. As shown in FIG. 4,
the base 34 further includes a bearing race 56 mounted inside the opening
50 and a pair of adjustable limit stops 58 and 60 mounted on a surface 62
of the base 34 near the opening 50. The base 34 also preferably includes
holes suitable for mounting it to a stable structure such as a mounting
bracket or the like as shown in FIG. 3.
The rotary joint 42 is sometimes herein called the base joint. When the
base joint 42 is assembled, the link 36 is rotatable about an axis through
the center of the opening 50 and perpendicular to the plane of the surface
62. The positions of the limit stops 58 and 60 are determined by the range
of rotational motion desired for the link 36 relative to the base 34.
Referring to FIGS. 1 and 17, a motor 61 is mounted to the base 34 to drive
the base joint 42, which is formed when the link 36 is connected to the
base 34. The motor 61 has an output shaft 63 shown in FIGS. 1, 2 and 17
that extends through a hole 65, best shown in FIG. 4, in the base 34. As
shown in FIGS. 1-5, a base joint pulley assembly 66 is fixed to the link
36 near the bearing 64. A drive cable 67, shown in FIG. 17, mounted to the
base joint pulley assembly 66 and to the output shaft 63 transfers
rotation of the motor output shaft 63 to the pulley assembly 66.
Referring to FIGS. 4 and 5, a bearing 64 is mounted to the link 36 for
mounting inside the bearing race 56 to form the joint 42. A preloaded,
four point contact, Gothic arch bearing functions satisfactorily to join
the link 36 to the base 34. Such bearings are commercially available.
Referring again to FIGS. 1-5, the base joint pulley assembly 66 is
preferably a sector pulley formed to comprise a pulley base 70 having an
outer rim 71 and a four piece cover 72. The outer rim 71 has a portion 71A
that spans a predetermined arc. The outer rim 71 has straight portions 71B
and 71C that engage the limit stops 58 and 60 on the base 34 to limit the
range of rotation of the joint 42. The pulley base 70, the outer rim 71
and the cover 72 enclose a cavity in which additional components are
mounted as described subsequently.
Referring to FIGS. 5 and 6, near end 74 of the arc 71A, the base joint
pulley assembly 66 includes a pair of tensioning idler pulleys 76A and 76B
mounted in the pulley base 70. Another pair of tensioning idler pulleys
78A and 78B, shown in FIG. 8, are mounted to the pulley base 70 near the
end 75 of the arc. The base joint pulley assembly 66 also includes a
termination pulley 79, shown in FIG. 7, mounted near the tensioning idler
pulleys 76A and 76B. A tension equalizing pulley 80, shown in FIG. 8, is
mounted near the tensioning idler pulleys 78A and 78B.
Referring to FIG. 6, the tensioning idler pulleys 76A and 76B are assembled
into the base joint pulley assembly 66 by first inserting one end of an
tensioning idler pulley shaft 81 into a passage in the pulley base 70. A
bushing 82 is placed on the shaft 81 adjacent the pulley base 70. The
tensioning idler pulley 76A, a divider bushing 83, the tensioning idler
pulley 76B and a bushing 84 are mounted on the shaft 81 as shown in FIG.
6. The shaft 81 is retained in position by placing its other end in a
passage in the cover 72 and then securing the cover 72 to the pulley base
70 with suitable fasteners (not shwon).
Referring to FIG. 7, the termination pulley 79 is mounted on a shaft 85
having a threaded bore (not shown) therein. An adjustment screw 86 extends
through a slot 87, shown in FIG. 7, in the pulley base 70. A bushing 88,
the termination pulley 79 and a bushing 89 are placed on the shaft 85,
which is then aligned with the adjustment screw 86 so that it may be
engaged with the threaded bore in the pulley shaft 85. The head of the
adjustment screw 86 engages the edges of the slot 87 to secure the pulley
shaft 85 and the termination pulley 79 in a selected position in the
pulley base 70. The slot 87 allows the termination pulley block 79 to be
moved relative to the tensioning idler pulleys 76A and 76B and thereby
provides for a coarse adjustment of the cable pre-tension.
FIG. 8 illustrates how the tension equalizing pulley 80 and the tensioning
idler pulleys 78A and 78B are mounted in the base joint pulley assembly
66. A curved slot 90, best shown in FIG. 5, and a circular passage 91 are
formed in the pulley base 70. A circular passage 92 is formed in the cover
72 opposite the circular passage 91. A tension arm 93 has an equalizer
pulley shaft 94 and a tensioning idler pulley shaft 95 extending therefrom
generally parallel to one another. The tensioning idler pulley shaft 95
includes projections 96 and 97 that extend from its ends. A bushing 98 has
a hollow projection 99 that fits closely in the circular passage 92. The
projection 96 fits closely in the hollow projection 99 to mount an end of
the tensioning idler pulley shaft 95 to the pulley cover 72. A bushing
100, the tensioning idler pulley 78B, a divider bushing 101, the
tensioning idler pulley 78A and a bushing 102 are placed on the tensioning
idler pulley shaft as shown in FIG. 8. The bushing 108 includes a hollow
projection 103 that extends into the circular passage 91. The projection
97 of the tensioning idler pulley shaft 95 extends into the bushing 102 to
mount tensioning idler pulley shaft 95 between the pulley base 70 and the
pulley cover 72.
Still referring to FIG. 8, the tension equalizing pulley 80 is mounted on
the tension equalizer pulley shaft 94 between a pair of bushings 104 and
105. An adjustment screw 106 extends through the curved slot 90 for
threaded engagement in the tension equalizing pulley shaft 94. The head of
the adjustment screw 106 engages the edges of the curved slot 90 to hold
the tension equalizing pulley shaft 94 in a set position. Fine cable
pre-tension adjustments can be made by engaging a suitable torque wrench
(not shown) with the end of the projection through the circular passage
91, rotating the wrench to the desired tension level, and then securing
the adjustment screw 106 within slot 90.
Referring again to FIGS. 2 and 5, at the end of the link 36 opposite the
base joint pulley assembly 66 there is a torso shaft 110 that includes a
cylindrical bore 112. The centerline of the cylindrical bore 112 is
perpendicular to and intersects the axis of rotation of the joint 42. A
preloaded matched set of back-to-back duplex bearings 114 are mounted in
the cylindrical bore 112 and separated by precision ground spacers.
Referring to FIGS. 1-3, 5 and 9, the link 37 is mounted to the link 36 at
the rotary joint 43, which is sometimes called the shoulder joint.
As shown in FIG. 9, a shoulder joint shaft 116 extends from the link 37
near an end 117 thereof. The joint 43, best shown in FIGS. 1-3, is
assembled by placing the shoulder joint shaft 116 into the cylindrical
bore 112 containing the matched duplex bearing set 114 and securing the
inner races with a clamp 118.
Referring again to FIG. 5, the link 36 includes a bracket 119 for mounting
a motor 120, shown in FIG. 2, that drives the rotary joint 43. A stop 122,
shown in FIG. 5, may be attached to the link 36 for limiting the range of
motion of the link 37 relative to the link 36. The location of the stop
122 depends upon the range of motion desired for the rotary motion of the
link 37 about the joint 43.
Referring to FIGS. 1-3 and 9, the link 37 is an elongate member preferably
formed of hollow aluminum tubing to have a square cross section with high
strength and low mass. A shoulder pulley assembly 124 is mounted to the
link 37 to have an axis of rotation coincident with the axis of the
shoulder joint shaft 116. The shoulder pulley assembly 124 is similar to
the base joint pulley assembly 66. Referring to FIGS. 9 and 17, the
shoulder pulley assembly 124 includes a cable termination block 126, a
pair of tension idler pulleys 128A and 128B, a tension equalizing pulley
130 and two equalizing idler pulleys (not shown). The shoulder pulley
assembly 124 may include a limit stop pin 134 that limits its range of
angular motion.
The motor 120 and the shoulder pulley assembly 124 are located on opposite
sides of the bracket 119. Referring to FIG. 17, the motor 120 has an
output shaft 129 that passes through a hole 131, shown in FIG. 5, in the
bracket 119. A drive cable 133 shown in FIG. 17 is routed over the tension
equalizing pulley 130, the two tension idler pulleys (not shown) near
tension equalizing pulley 130, around the motor shaft 129 (three wraps),
and over the tension idler pulleys 128A and 128B with both ends of the
cable terminating at the cable termination block 126. Therefore, rotation
of the motor shaft 129 rotates the shoulder pulley assembly 124 about the
axis of the joint 43, which is the center line of the cylindrical bore
112.
Referring to FIGS. 1-3 and 9-11 the force-reflecting hand controller 30
includes a rotary joint 44, also called the elbow joint, that provides a
means for rotating the link 38 relative to the link 37. The joint 44 is
formed by the union of a three stage cable drive reduction assembly 138
shown in FIG. 11. The assembly 138 is mounted to the end of link 137
opposite the end 117 to an output pulley assembly 151 that is mounted to
link 38.
Referring to FIGS. 1, 9-11, and 16, the three stage cable drive reduction
assembly 138 includes a frame 141 and three reduction pulleys 142-144
mounted within the frame 141 on axes parallel to each other. The pulleys
142-144 are arranged to provide drive train reduction in close proximity
to rotary joint 44 for better transmission efficiency. The pulleys 142-144
reduce to smaller diameter shafts and mount to the frame 141 by means of
three pairs of thin section bearings (not shown) and extend outward from
the frame 141 as pulleys 146-148 of reduced diameter.
Also included within the cable drive reduction assembly 138, and referred
to in more detail hereafter, is a bore 149 and two shafts that mount
stacks of guide pulleys 197A and 197B within frame 141. The guide pulleys
197A and 197B provide means for transmitting cables 198A, 198B, 199A,
199B, 200A, 200B, shown in FIGS. 16-19, that actuate the orientation
degrees of freedom joints 45-47, so that the cables traverse the joint 44
fully decoupled and independent from any relative rotation of links 38 and
37 about joint 44. The center of bore 149 is coincident with the axis of
rotation for joint 44 and provides means for mounting a preloaded matched
duplex bearing set.
Referring to FIGS. 1-3, 10, 12, 13 and 16, the output pulley assembly 151
of the rotary joint 44 includes a pulley base 152 having a shallow cavity
158 that contains a system of smaller cable tensioning pulleys described
in more detail hereafter. Included in the output pulley assembly 151 is a
hollow shaft 166, best shown in FIG. 12, whose bore provides a pathway for
transmission cables for rotary joints 45-47 traversing the joint 44. The
shaft 166 extends outward from the center of pulley base 152 above the
cover plate 155A and, when mounted to the three stage cable drive
reduction assembly 138, engages the duplex bearing set mounted within the
bore 149 of frame 141. When assembled, the center of the bore of shaft 166
is coincident with the axis of rotation for the joint 44 and allows
relative motion of the link 38 with respect to the ink 37.
A motor 204, shown in FIG. 2, mounted to the link 37 near the end 117, is
arranged to provide output torque to drive the rotary joint 44 through a
three stage cable drive train. The drive train for the joint 44 includes a
split hub pulley (not shown) mounted onto the output shaft of the motor
204, steel drive cables traversing the hollow length of link 37 and
connecting the pulley 144 to the split hub motor pulley with a 1:1 drive
ratio. The pulley 144 reduces to the diameter of the pulley 147 and
engages pulleys 143 and 142 via another steel cable with a 2.8:1 drive
ratio. The pulleys 142 and 143 reduce in diameter to the pulleys 146 and
148 and engage the output pulley assembly 151 via a set of two steel cable
segments with a 6.6:1 drive ratio. The result is an overall motor to
output pulley drive ratio of 18:1.
Since a single motor 204 produces both the antagonistic forces required to
actuate joint 44, as on other joints, means for pre-tensioning the cable
drives to a level at least one half their maximum expected load is
provided to prevent the cables from becoming slack under maximum load and
to increase the apparent transmission stiffness. The first stage of the
three stage cable drive train for rotary joint 44 is pretensioned by
loosening the two screws locking the split hub pulley halves together,
rotating the pulley halves relative to one another by holding one
stationary and applying a torque wrench to a hex slot cut in the other
and, while attaining the proper pre-tension, re-tightening the two screws.
Referring to FIGS. 10, 12, 13 and 16 the two steel cable segments included
in the last stage of the three stage drive train that actuates joint 44
are routed as follows. One end of the first cable segment is terminated
and inserted into a slot provided in the end of pulley 146 and then
wrapped around the pulley 146 and engaged with the output pulley assemby
151. The cable wraps partially around the output pulley assembly 151,
around a lower tension idler pulley 164A, around a stationary tension
equalizing pulley (not shown) around an upper tension idler pulley 164B,
back over the outer rim 156 of the pulley base 152, and then back around
the pulley 146, terminating in the same slot as before. Spiral grooves in
the surfaces of the pulleys 146 and 148, shown in FIG. 11, cause the cable
to track properly across the smooth outer surface of the output pulley
assembly 151 as the pulleys rotate relative to one another. One end of the
second segment of cable constituting the third stage is terminated and
inserted into a slot in the end of output pulley 148. The cable wraps
around the pulley 148 and then wraps around the pulley 152 in the opposite
direction from before, over the lower tension idler pulley 165A of FIGS.
12 and 13, around a tension equalizing pulley mounted to a tensioning arm
170 by means of a shaft 162, around the upper tension idler pulley 165B,
back over the outer rim 156 of pulley base 152, and then back around
pulley 148, terminating in an end slot 168 provided in the pulley 148.
Referring to FIGS. 12 and 13, the lower tension idler pulley 164A and the
upper tension idler pulley 164B are separated by a bushing and mounted to
a shaft 190. The shaft 190 is fixed to output pulley base 152 at the
bottom and held in place by cover 155B at the top. The two tension idler
pulleys 165A and 165B are mounted in a similar manner to shaft 194. The
tensioning arm 170 has a centrally located bore 174 into which slides a
bushing 167 which in turn slides over the hollow shaft 166 as best shown
in FIGS. 12 and 13.
The routing method described above results in the third stage having two
double spans of cable which increases the transmission stiffness. These
cable spans can be accurately pre-tensioned by removing cover plate 155A,
loosening a locking screw 180 shown in FIG. 14 that secures the tensioning
arm 170 to pulley 152 at threaded hole 192, locking tensioning arm 170 to
frame 141, rotating link 38 relative to link 37, and then re-tightening
locking screw 180.
Referring to FIGS. 14, 18 and 19 assembly of the link 38 includes mounting
a plurality of guide pulley assemblies 196A, 196B and 196C in the end of
the link 38 near the joint 44. These guide pulley assemblies 196A, 196B
and 196C cooperate with the pulleys 197A and 197B to route cables 198A,
198B, 199A, 199B, 200A, 200B for the joints 45-47 through the joint 44 and
the link 38.
Referring to FIGS. 14, 18 and 19, guide pulley assemblies 196A, 196B and
196C for the joints 45-47 are mounted in the link 38. The guide pulley
assemblies 196A, 196B and 196C preferably include two pulleys each as
shown in FIG. 19. Guide pulley assemblies 197A and 197B that each comprise
a stack of three pulleys are mounted to the link 37.
A first length of cable 198A for the joint 45 passes around a pulley (not
shown) in the stack 197A, and a second length of cable 198B for the joint
45 passes around a pulley in the stack 197B. The cables 198A and 198B are
then routed through the hollow shaft 166 to the guide pulley assembly
196A. Similarly, cable lengths 199A and 199B for the joint 46 are routed
around corresponding pulleys in the stacks 197A and 197B, respectively, to
the guide pulley assembly 196B. Cable lengths 201A and 201B for the joint
47 are routed around corresponding pulleys in the stacks 197A and 197B,
respectively, to the guide pulley assembly 196C.
Referring to FIGS. 1-3, 15A and 15B the handgrip 32 is mounted in a gimbal
assembly 220. The gimbal assembly 220 is mounted to an end 224 of the link
38 as best shown in FIGS. 1-3 and 14. The link 39 of FIG. 1 may be formed
as a generally semicircular gimbal yoke 226. The link 40 may be formed as
a circular gimbal ring 227. The gimbal yoke 226 is mounted to be rotatable
about the longitudinal center line of the link 38 at the rotary joint 45.
The joint 45 includes a bearing housing 230 in a gimbal mounting bracket
232 and a pulley 234. The joint 45 may also include a limit stop (not
shown). A shaft 236 fixed to the gimbal yoke 226 passes through the gimbal
mounting bracket 232. The pulley 234 for the joint 45 is fixed to the
shaft 236, and the bracket 232 is mounted to the end of the link 38. A
pair of guide pulleys 240 and 242 are mounted to the bracket 232 to guide
the cables 198A and 198B to the pulley 234 from a motor 243 mounted to the
link 37.
The gimbal ring 227 has a peripheral flange 244 shown in FIGS. 1 and 15B.
The peripheral flange fits within slots formed in a pair of mounting
brackets 246 and 248 shown in FIGS. 1, 2, and 15B that are connected to
the gimbal yoke 226 at the joint 46. A gothic arch, x-contact bearing (not
shown) is mounted to the flange 244. The bearing has an inner race that is
clamped to the ring 227 by a secondary ring (not shown). The bearing has
an outer race that fits within slots formed in the brackets 246 and 248
for the joint 46. The two brackets 246 and 248 mount to the yoke 226 with
a preloaded angular contact bearing (not shown).
Referring to FIGS. 1, 2, 15A and 15B, the joint 46 includes a pair of
pulleys 250 and 252 fixed to the brackets 246 and 248, respectively. The
pulleys are connected via the cable lengths 199A and 199B to a motor 254
that is mounted to the link 37 near the end 117 as shown in FIGS. 1-3. The
cable lengths 199A and 199B pass through the joint 45. As shown in FIG.
15B, a pair of guide pulleys 256 and 258 direct the cable length 199A and
199B from the vicinity of the joint 45 to the pulleys 250 and 252 that are
used to drive the joint 46. Additional guide pulleys may be used as
necessary to direct the cable lengths 199A and 199B through the gimbal
yoke 226 to the pulleys 250 and 252 without interfering with motion of the
gimbal ring 227.
The pulleys 250 and 252 are connected to the flange 244 via a thin section
of the gothic arch bearing. The gimbal ring 227 is rotatable about a line
perpendicular to the plane of FIG. 1. The handgrip 32 is fixed to the
gimbal ring 227 and is, therefore, rotatable about three mutually
perpendicular axes.
The rim of the gimbal ring 227 functions as the drive pulley for the joint
47. The cable lengths 200A and 200B for the joint 47 pass from a motor 260
mounted to the link 37, as shown in FIGS. 1-2, through the interior of the
link 37 to the joint 44. The cable lengths 200A and 200B then pass through
the joint 44 as described above along the axis thereof to the end of the
link 38. Guide pulleys 262 and 264 then direct the cable lengths 200A and
200B for the joint 47 from the vicinity of the joint 45 to guide pulley
assemblies 266 and 268 that are used to guide the cable lengths 200A and
200B to the ends of the gimbal ring 227. The cable lengths 200A and 200B
then pass through the centers of the pulleys 250 and 252 to a pair of
small guide pulleys 270 and 272, shown in FIG. 15B, that direct the cables
to the rim of the gimbal ring 227.
Joint 44 preferably includes a 3-stage drive reduction mechanism to provide
the desired stiffness goals. The other five joints in the force reflecting
hand controller 30 may have only single stage drives.
The links 36-38 and rotary joints 42-44 allow translational motion of the
handgrip 32 while the links 39-41 and the joints 45-47 allow orientation
of the handgrip 32. The rotary joints 42 and 43 have perpendicular axes
that intersect. The joint 44 has an axis of rotation that is parallel to
the axis of the joint 43. The joint 44 is displaced from the joint 43 by
about 15 inches.
The motors for the joints 44-47 are mounted on the link 37 near the end
117. The cable circuits for each of the joints 45-47 should be
pretensioned to prevent backlash in the mechanisms.
The combined weights of the motors thus act to partially counter balance
the weight of the links 37. The motors preferably are brushless DC torque
motors having 1000 line, dual quadrature, incremental optical encoders
mounted directly on their shafts.
The actuator transmission design includes a unique steel-cable routing
scheme. This type of transmission, as opposed to geared transmissions,
provides drive mechanisms with virtually no backlash. The cable drive
system also allows three other very significant design features: (1) the
inertial effects from the mass of each motor are greatly reduced because
the motors are all mounted near the base of the hand controller, (2) the
design has no kinematic offsets, and (3) the steel-cable routing design
permits all six joints to be fully decoupled from one another such that
each joint rotates completely independent of all others. The links are
physically offset, which allows the hand controller to fold up into a
compact unit when not in use.
Several design parameters are of particular interest in evaluating the
utility and effectiveness of the FRHC 30. These parameters include
positional resolution, dynamic range of the force output, friction levels,
inertia, backdrivability, backlash, stiffness, dynamic mechanical
response, and resonant frequencies.
The overall hand controller mechanical stiffness was a primary concern
during the design process. This is evident at several critical locations
throughout the design. Joints 42 and 45 preferably include single
preloaded, gothic-arch, x-type bearings. Joints 43 and 44 preferably
include a matched pair of preloaded, back-to-back duplex bearings. Links
37 and 38 preferably are made of aluminum tubing with a square
cross-sectional shape which is significantly stiffer than round tubing of
the same basic size. The steel transmission cables, used in all six
joints, preferably are pretensioned. Each joint steel cable circuit can be
accurately pretensioned. The transmission circuits for joints 42 and 43
preferably include double spans of steel-cable in order to reach desired
stiffness levels. The force reflecting hand controller 30 provides
kinesthetic feedback to the operator. The act of moving a telerobot's
mechanical hand in the performance of a task is directly related to the
physiological motor sensations that would occur if the operator were
performing the task with his own hand. The intrinsic eye-hand coordination
of the human operator is fully utilized, making the performance of the
task at the remote work site highly intuitive to the operator.
The force reflecting hand controller 30 provides high-fidelity force
feedback, so that the it has a good dynamic force output capability. Small
feedback forces to the operator are not obscured by friction levels, and
yet the force reflecting hand controller 30 can also output relatively
large forces. Moreover, the forces and torques transmitted to the operator
are crisp and distinguishable.
Because the force reflecting hand controller 30 is kinematically simple,
the structure of the FRHC 30 is simple to describe mathematically. The
FRHC 30 has no kinematic joint offsets and several of the joint axes
intersect at right angles thereby making it one of the simplest
configurations possible for a six degree of freedom manipulator. This
simple configuration helps to minimize the computer time required to
calculate the location of the center of the handgrip 32 relative to a
fixed reference location.
One feature of the FRHC 30 that greatly simplifies the control algorithms
is that all six degrees of freedom are mechanically decoupled. This means
that each of the six mechanical joints on the FRHC 30 rotate independently
of all others. Therefore, the control algorithms that determine the joint
torques are direct and do not need to make the otherwise necessary
compensation.
The use of preloaded bearings and pretensioned cables allows the force
reflecting hand controller 30 to have zero joint backlash. Having no
backlash, or free play, is an important feature because it eliminates
position deadband in the mechanism and increases the stability of the
control system.
Minimizing friction was an important consideration during the FRHC 30
design. The FRHC 30 according to the present invention is run open loop,
i.e., the actual output forces to the operator are not measured or fed
back to the control algorithms. Therefore, friction becomes a limiting
factor in determining the smallest commandable output force and affects
the force resolution. Large friction forces could deflect the operator
from an intended input path and, in severe cases, could degrade the
backdrivability of the hand controller.
The hand controller according to the present invention is designed to have
maximum stiffness and responsiveness. This attention to structural
stiffness improves the quality and clarity of the forces the operator
feels because it shortens the response time of the mechanism and also
contributes to control system stability.
The work envelope of a hand controller refers to the three-dimensional
space through which the operator is able to move the handgrip. In special
mounting configurations this work envelope coincides directly with the
range of motion for the human operator's arm. Therefore, the FRHC 30 can
follow almost any motion of the human operator's hand over its entire
reach.
The positional resolution, i.e., the smallest detectable motion at the
handgrip 32, changes slightly across the work volume due to the geometry
involved. At near full extension, the FRHC 30 has its least resolution.
However, even in this worst case configuration, the positional resolution
is still better than 0.002 of an inch. The positional resolution increases
as the handgrip is moved closer to the axis of the joint 42.
The dynamic range of output forces and torques provides insight into the
quality and clarity of the forces that are reflected back to the person
operating the FRHC 30. The dynamic range is defined as the maximum
commandable output force divided by the minimum commandable output force.
The output forces in the X, Y, and Z directions are position dependent and
are inversely proportional to the distance out from the axis of the joint
42. In the worst case, when the hand controller is fully outstretched and
operating in gravity, the FRHC 30 can output feedback forces to the human
operator ranging from about 3 ounces up to 67 ounces. Larger forces are
possible as the handgrip 32 is moved closer to the axis of the joint 42.
In space applications, the maximum output forces in the plane defined by
the links 37 and 38 will be significantly higher since there are no
gravitational forces to counteract.
The friction forces the operator feels vary throughout the work volume
depending again on the distance between the handgrip and the axis of the
joint 42. With the hand controller near full extension, these friction
levels are about 3 ounces in any direction and slightly increase as the
handgrip is moved closer to the axis of the joint 42. The friction levels
for the three orientation degrees-of-freedom are constant and are about 6
in-oz. for each of the joints 45 and 46 and about 13 in-oz. for the joint
47.
The overall mass of the force reflecting hand controller 30 is preferably
kept as small as possible without compromising structural ruggedness. A
working prototype has a total weight of 32 lbs. The motors, which
collectively contribute almost half the overall mass, are mounted near the
base of the hand controller, which greatly reduces their inertial effects.
The low overall inertia and friction levels result in the hand controller
mechanism being very backdrivable so that forces encountered by the robot
arm are accurately transmitted to the handgrip 32.
At over 4 cu. ft. the FRHC 30 has a work envelope that more than doubles
that of previous hand controllers. This was done in order to maintain its
applicability to a wide variety of tasks. Yet the FRHC 30 can be folded up
and compactly stowed in a case with a volume of only 1.8 cu. ft.
The FRHC 30 has a rugged structural design that is necessary for the
rigorous demands of space flight. The mechanical stiffness of the device
plays a role in establishing the fidelity of feedback forces to the human
operator. For example, under a 9.4 lb static test load there was a 0.032
inch deflection at the end of the link 37. This represents a torsional
spring constant (k.sub.t) about the axis of the joint 43 of more than 1970
in-lbs/deg. This torsional spring constant may be used to provide an
initial estimate of the structural resonant frequency about the axis of
the joint 43 of over 21 Hz.
Frequency response tests indicate natural frequency values for the FRHC 30,
within the following ranges: joint 42 at 27-29 Hz, joint 43 at 27-33 Hz,
and joint 44 at 37-40 Hz. These natural frequency values are approximately
two to three times higher than those found in previous hand controller
designs.
The FRHC 30 is an intuitive, highly versatile, human interface to complex
multi-degree-of-freedom dynamic machines. As a position input device with
force output capabilities, the FRHC 30 is the fundamental and natural
interface a human operator needs to manipulate multi-dimensional spatial
relationships where force cues can help associate a coordinated response.
As such, the FRHC 30 has utility as a useful man/machine interface in
applications other than the control of teleoperated robotic arms.
The FRHC 30 according to the present invention may have application in
several technologies. For example, the FRHC 30 may be used to control the
movements of underwater robots for locating and investigating objects on
deep ocean bottoms. These submersible robots can travel in three
directions (forward/backward,up/down and side to side) and rotate about
three axes (roll, pitch and yaw). Presently several joysticks are
necessary to pilot these submersible robots, whereas a single force
reflecting hand controller 30 can perform several motions simultaneously.
Using the force reflecting hand controller 30 instead of joysticks could
greatly increase the ease and precision with which such machines may be
commanded. For example, an underwater robot could be moved forward and up
and rotated all at the same time.
Use of the force reflecting hand controller 30 could simplify the operation
of a helicopter. Currently a pilot must use both hands and both feet to
fly a helicopter. These complex maneuvers require great skill and
coordination. The force reflecting hand controller 30 provides a complete
flight control input device that would allow a pilot to fly a helicopter
with only one hand.
Another use of the force reflecting hand controller 30 is in computer
graphics applications. Advanced computer graphics software now permits the
creation of three dimensional objects that may be manipulated relative to
the point of view of the user and relative to other objects. The user can
zoom in, zoom out, move the objects up and down or from side to side. It
is also possible to reorient the roll, pitch and yaw axes of an object
displayed on a computer video monitor. Several new input devices have been
developed to make this type of object manipulation less cumbersome, but
these devices are limited to two or three dimensions at a time instead of
providing the six degree of freedom control required to position and
orient an object in three dimensional space.
The force reflecting hand controller 30 may be interfaced with a computer
to allow a user to move and orient graphic images as easily and
intuitively as if the user had actually manually manipulated the objects
that the images represent. The capability of the force reflecting hand
controller 30 to provide force feedback would enable a user to manually
sense contact between objects being manipulated on a screen. This
capability could greatly enhance the sensory bandwidth of human interface
with graphics work stations.
Still other applications of the force reflecting hand controller 30 are in
the nuclear industry and controlling remotely piloted vehicles.
The geometry and kinematics of the force reflecting hand controller 30 and
a teleoperator that it is used to control need not be identical. The
positional control relationship between the force reflecting hand
controller 30 and the teleoperator must be established through
mathematical transformation of joint variables measured at both the force
reflecting hand controller 30 and the teleoperator in real time. Forces
and torques sensed at the mechanical hand of the teleoperator must be
resolved into appropriate joint drive signals for the force reflecting
hand controller 30 through mathematical transformations in real time to
give the operator's hand a force/torque sensation that corresponds to the
same forces and torques sensed at the mechanical hand. The particular
mathematical transformations between the handgrip and the mechanical hand
depend on the structural details of the teleoperator and can be done by
those skilled in the art. For example, Bejczy and Salisbury, Controlling
Remote Manipulators Through Kinesthetic Coupling, Computers in Mechanical
Engineering, July, 1983, pp. 51-60 describe the mathematical
transformation between a previous force reflecting hand controller and a
particular mechanical arm.
The structures and methods disclosed herein illustrate the principles of
the present invention. The invention may be embodied in other specific
forms without departing from its spirit or essential characteristics.
Therefore, the described embodiments are to be considered in all respects
as exemplary and illustrative rather than restrictive. Therefore, the
appended claims rather than the foregoing description define the scope of
the invention. All modifications to the embodiments described herein that
come within the meaning and range of equivalence of the claims are
embraced within the scope of the invention.
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